Electron discharge device



April '25, 1939. H. o. HARRIES ELECTRON DISCHARGE DEVICE Filed Aug. 12, 1936 INVENTOR -Wm ATTORNEYS Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE Application August 12, 1936, Serial No. 95,494 In Great Britain May 25, 1936 Claims.

them becomes substantially saturated; The invention is particularly but not exclusively concerned with discharge tubes of the above kind in which the distance between the aforesaid electrodes is definitely chosen to be about equal to the distance at which the rate of change of the.

distance curve is substantially zero. In the above-mentioned patents I have also described valves having their electrodes spaced as above in combination with the use of means for focussing or directing in any desired direction the electrons composing part or parts of the stream; and in which a substantial negative potential gradient between the two electrodes is partly 26 produced by a suitably positioned electrode which is at or about cathode potential.

The object of the invention is to combine the two last-mentioned characteristics, namely, directing the electrons and also producing a negative potential gradient by means of an electrode at or about cathode potential, by means having the advantages of simplicity of manufacture and cheapness and which may readily be freed from occluded gases during the normal manufacturing treatment of the tube. V

In order that the invention may be more clearly understood it will now be described by way of example with reference to the accompanying drawing, in which:-

Figure l is a side elevation of an electron discharge tube, the anode being broken away to Show the other electrodes, and

Figure 2 is a plan of Fig. 1.

Figure 3 is a circuit diagram.

Figure 4 is a graph showing the relation between the anode auxiliary electrode distance and the breakdown voltage.

Referring now to the drawing, the cylindrical anode I is supported by means of rods 2 which are secured at their lower end in the glass press 3. The'outer envelope 4 of the tube together with the glass press 3 are carried by a base 5. The auxiliary or accelerating electrode is formed of a pair of rods 6 and 1, one of which rods is secured at its lower end inthe glasspress 3.

Each of the rods 6 and 1 may be arranged to pass through plates 8 and 9 of insulating material, for example mica, which are carried by the rods 2 for theanode. These plates 8 and 9 serve to retain the auxiliary electrode in position. 5 The auxiliary electrode consists of a wire mesh formed by a winding of wire I on the rods 6 and I, and this may conveniently be given the substantially lenticular cross-sectional shape shown in Figure 2. The control grid comprises a wind- 0 ing of wire H on a pair of supports I2 and I3, one of which is retained in position by the insulating plates 8 and 9, and the other of which, l3, extends into the press 3. The auxiliary and control electrodes are of substantially the same 15 length as the anode although in Fig. 1 each is shown as being broken away over substantially half its length to avoid confusion with the other. The cathode l4 may be of the usual construction and may also be supported by means of the plates 20 8 and 9. The filament wires l5 may be respectively connected to leads l6 sealed in the press 3, and the usual leading-in wires for each of the other electrodes may be provided in the known manner. 5

The relative positions of the anode and auxiliary electrodes are determined by the distance curve illustrated in Fig. 4 in which the distance d of the anode from the accelerating electrode is applied against the breakdown voltage Eb, that 30 is to say, the anode voltage at which anode current becomes saturated. From this curve it will be seen that there is a critical distance of the anode from the auxiliary electrode at which the breakdown voltage is a minimum and 35 it is preferred to arrange the anode either at its critical distance or a distance at which the rate of change of the curve is positive or not more than slightly negative, since when the anode is so placed any secondary electrodes which may 40 be omitted from the anode are prevented by a spaced charge frompassing back to the auxiliary electrode.

According to the invention, and in the particular form of tube illustrated, four rod-like di- 45 recting electrodes are positioned in the space between the auxiliary electrode l0 and the anode I. These rod electrodes H, which may have substantially the same cross-sectional area as the support rods 6 and 1 or l2 and I3, may be 50 arranged in pairs on either side of the major axis of the auxiliary electrode I 0 and may also be suitably supported by passing through holes in the insulating plates 8 and 9. One of the rod electrodes I1 is extended downwards towards the 55 press and connected to a lead sealed therein, this lead being also, if desired, connected to the cathode of the valve. In the example shown this latter connection is effected by a. wire I8 connecting the cathode to one of the rods l1, all four rods being electrically connected together by further rods l9 and 20 which may be disposed either as shown above the plate 9 or if desired above or below the plate 8.

In this type of tube the electron discharge in the absence of the rods I1 passes towards the anode in two more or less fan-shaped beams, there being comparatively little discharge towards the anode in the general direction of the major axis of the control grid and accelerating grid. I have found that this partial spreading of the electron beam has a tendency to reduce the density of the stream between the auxiliary or accelerating electrode and the anode. Since it is essential that the anode should be positioned at the critical distance, that is to say the distance at which the rate of change of the distance curve is positive or not more than slightly negative, a lowered density of the electron stream results in an increased anode diameter. By positioning the rod electrodes I! so that the electron beam passes therebetween the electrons are constrained to move towards the anode in a comparatively confined path, thus increasing the density of the stream and enabling the anode diameter to be reduced.

In general it may bedesirable to position the electrodes ll outside the area between the control grid and its projection upon the face of the anode.

A further advantageous effect is obtained in that the said rod electrodes ll assist in'the production of a negative potential gradient between the auxiliary electrode Ill and the anode I, thus further decreasing the anode diameter at which the anode is at the said critical distance.

The type of valve shown in Figures 1 and 2 can be conveniently constructed so as to have the following dimensions- Cathode.--l.5 mms. x 1 mm. x 35 mms. Control grid:

Supports.--l.5 mms. diameter. Wire winding.-0.1 mm. diameter wire wound 15 turns per cm. Accelerating grid:

Support rods.1 mm. diameter. Wire winding.0.1 mm. diameter wire wound 9.5 turns per cm.

Rod directing eZectr0des.-0.75 mm. diameter.

The rods of each pair between the accelerating electrode and the anode 1.3 cms. apart. Distance between the rods of each pair 4.8

mms.

'Anode.22 mms. diameter. 26 mms. long.

The anode may conveniently be of nickel sub-' jected to a carbonizing treatment.

It may here be mentioned that in an exactly similar valve, excepting only that the rod directing electrodes are omitted; has a critical anode diameter of 27 mms.

Valves constructed according to the invention may be employed in any of the well-known ways, the circuit diagram shown in Figure 3 being typical. In this diagram the input signal to be amplified is applied across the terminals A and B, the terminal A being connected to the control grid l l whilst the terminal B is connected to the cathode through a resistance shunted by a condenser. The directing electrodes are connected directly to the cathode either externally of the valve or internally. The auxiliary electrode may be held at a positive potential by being connected to the positive pole of a source of direct current, the anode being fed from the same source through the primary winding 01 an output transformer the secondary of which is used, for example, to energize the speech coil of a loud speaker.

When the rod electrodes I1 are not connected to the cathode within the valve they may be brought out to a separate terminal so that they may be given a potential of the order of the cathode potential, whilst not being connected directly thereto. A valve having the dimensions given above may be employed in the above-described circuit, in which case the following electrical values will be found suitable:

High tension potential volts.. 250 Mean anode current milliamperes 32 Cathode bias resistance ohms 250 Shunt condenser microfarads 25 It must be understood that the above circuit diagram represents a simple form of power output stage, but the valve may be used in other ways, for example a pair of valves may be arranged in push-pull or in any of the other wellknown circuit arrangements.

It must also be understood that the invention is not limited to the constructional embodiment above described, which is merely given by way of example, but it also extends to tubes in which the electrodes have difierent configurations. Further, the rod electrodes, instead of being positioned between the auxiliary electrode and the anode, may in certain cases be positioned between the accelerating electrode and the cathode.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. An electron discharge device comprising a cathode, a control electrode, an auxiliary electrode, an anode spaced from said auxiliary electrode by a distance approximating the distance at which a minimum anode voltage produces anode current saturation, rod-like electrodes independent of said control and auxiliary electrodes for directing electrons in a comparatively confined path towardsaid anode, and electrical connections between said rod-like electrodes and said cathode.

2. An electron discharge device comprising a cathode, a control electrode, an auxiliary electrode, an anode spaced from said auxiliary electrode by a distance approximating the distance at which a minimum anode voltage produces anode current saturation, and rod-like electrodes independent of said control and auxiliary electrodes for directing electrons in a comparatively confined path toward said anode, said rod-like directing electrodes being positioned outside the area between the control electrode and its projection on said anode.

3. An electron discharge device comprising a cathode, an auxiliary electrode of substantially lenticular cross-section surrounding said cathode, a control grid of substantially lenticular crosssection positioned between said cathode and said auxiliary electrode, an anode of substantially cylindrical form surrounding saidauxiliary electrode and being spaced therefrom by a distance approximating the critical distance at which the minimum anode voltage produces anode current saturation, and four rod-like electrodes independent of said control and auxiliary electrodes spaced in pairs between said cathode and anode for directing the electrons in a comparatively confined path between each pair of rod-like elec trodes toward said anode.

4. An electron discharge device comprising a cathode, an auxiliary electrode of substantially lenticular cross-section surrounding said cathode, a control grid of substantially lenticular crosssection positioned between said cathode and said auxiliary electrode, an anode of substantially cylindrical form surrounding said auxiliary electrode and being spmed therefrom by .a distance approximating the critical distance at which the minimum anode voltage produces anode current saturation, and four rod-like electrodes independent of said control auxiliary electrodes spaced in pairs between said auxiliary electrode and said anode for directing the electrons in a comparatively confined path between each pair or rod-like electrodes toward said anode.

5. An electron discharge device comprising a cathode, an auxiliary electrode of substantially lenticu lar cross-section surrounding said cathode, a control grid of substantially lenticular cross-section positioned between said cathode and said auxiliary electrode, an anode of substantially cylindrical form surrounding said auxiliary electrode and being spaced therefrom by a distance approximating the critical distance at which the minimum anode voltage produces 

